1. Field of the Invention
The present invention relates to a small imaging lens for forming an optical image on a solid-state image sensing device such as a CCD type image sensor or CMOS type image sensor, and an imaging apparatus using the same.
2. Description of the Related Art
Imaging apparatuses using solid-state image sensing devices such as CCD (Charge-Coupled Device) type image sensors and CMOS (Complementary Metal-Oxide Semiconductor) type image sensors include digital still cameras, digital video cameras, and the like. Imaging apparatuses using such solid-state image sensing devices are suitable for miniaturization, and hence have recently been mounted in compact information terminals such as cellular phone sets. With increases in the miniaturization and pixel density of solid-state image sensing devices, demands have arisen for smaller and higher-performance imaging lenses to be mounted in these imaging apparatuses. As imaging lenses used for such an application, 4 element/3 group lenses each sequentially including, from the object side, an aperture stop, a first lens group having positive refracting power and including a cemented lens, a second lens group having an aspherical shape, and a third lens group having aspherical shape which are sequentially arranged from the object side is known, which are higher in performance than one or two element lenses. Among such lenses, a lens whose total length (the on-axis length from the aperture stop to the image-side focal point) is small, in particular, is disclosed in, for example, Japanese Patent Application Unexamined Publication (Kokai) No. 2002-228922.
The lens disclosed in Japanese Patent Application Unexamined Publication (Kokai) No. 2002-228922 is of a type which is designed to achieve miniaturization of an imaging lens by having an aperture stop placed nearest to the object side, a cemented lens as the first lens group which is constituted by positive and negative lenses, and aspherical lenses as the second and third lens groups, and letting the first lens group mainly contribute to the refracting power of the whole imaging lens system. However, as an imaging lens having such an arrangement, i.e., an arrangement in which a positive lens group having strong refracting power is placed near an aperture stop nearest to the object side, is reduced in total length, the exit pupil of the whole imaging lens system is brought near to the image-side focal plane, resulting in difficulty in obtaining good image-side telecentric characteristics. On the other hand, obtaining good image-side telecentric characteristics makes it difficult to perform aberration correction.